This invention relates generally to printers and more particularly concerns printers with an ink supply, and monitoring of the level of ink in the ink supply. The invention is disclosed particularly in relation to an ink jet printer having a disposable ink jet print head containing an ink supply.
Exemplary of printers having a consumable ink supply are ink jet printers which apply droplets of ink onto a medium to effect printing. It would be useful to know the level of ink available for printing in such a printer in order to prevent, for example, exhaustion of the ink supply in the course of printing a page.
There have been ink jet printers which have provided "ink low" indications. Early ink jet printers had ink reservoirs; and they used floating contacts, limit switches or thermistors in a number of ink level sensing schemes. In today's "drop-on-demand" ink jet printers, at least one such printer uses a reservoir float for an "ink low" sensor, together with a lifetime print head and replaceable ink cartridges connected to that print head.
However, the majority of lower cost ink jet printers use disposable cartridges including both print head and ink. The cartridges are very inexpensive but do not lend themselves readily to previously used ink level sensing approaches, for reasons such as the small size and low price point of these cartridges.
Ink jet printers utilizing such disposable print head cartridges generally do not provide ink level sensing. If there is no ink level indication provided to the user of a printer, there will be inaccurate or complete lack of warning before a cartridge runs out of ink. In such a case the ink may run out in the course of printing a page, and then the print job must be redone.
It is the general aim of the invention to provide ink level monitoring in an ink jet printer which utilizes replaceable ink cartridges. The invention is particularly suited for use in ink jet printers which employ removable and disposable print head and ink cartridges.
In carrying out the invention, a printer is provided which includes a disposable print head with an ink supply, the print head being actuatable to dispense ink from the ink supply onto a record medium. The printer further includes means for maintaining a cumulative record of actuations of the print head and means which are responsive to this cumulative record for causing a physical change in the print head.
In one embodiment of the invention, to be described hereinafter, the record of actuation of the print head is maintained in a memory which periodically receives a count of ink drops to be fired by the print head. In this exemplary printer, the print head includes a number of resistors which are periodically driven to an open circuit condition as the droplet count in the memory increases. The printer is capable of detecting the condition of the resistors in the print head in order to provide an indication of the ink level in the print head.
Further advantages and uses of the invention will become apparent in the following detailed description, with regard to which: